Title:
Hot methanol from the inner region of the HH 212 protostellar system

Abstract: The mechanisms leading to the formation of disks around young stellar objects
(YSOs) and to the launching of the associated jets are crucial to the
understanding of the earliest stages of star and planet formation. HH 212 is a
privileged laboratory to study a pristine jet-disk system. Therefore we
investigate the innermost region ($<100$ AU) around the HH 212-MM1 protostar
through ALMA band\,7 observations of methanol. The 8 GHz bandwidth spectrum
towards the peak of the continuum emission of the HH 212 system reveals at
least 19 transitions of methanol. Several of these lines (among which several
vibrationally excited lines in the v$_{\rm t}=1,2$ states) have upper energies
above 500 K. They originate from a compact ($<135$ AU in diameter), hot ($\sim
295$ K) region elongated along the direction of the SiO jet. We performed a fit
in the $uv$ plane of various velocity channels of the strongest high-excitation
lines. The blue- and red-shifted velocity centroids are shifted roughly
symmetrically on either side of the jet axis, indicating that the line-of-sight
velocity beyond 0.7 km s$^{-1}$ from systemic is dominated by rotational
motions. The velocity increases moving away from the protostar further
indicating that the emission of methanol is not associated with a Keplerian
disk or rotating-infalling cavity, and it is more likely associated with
outflowing gas. We speculate that CH$_3$OH traces a disk wind gas accelerated
at the base. The launching region would be at a radius of a few astronomical
units from the YSO.